Heartworm prevention is a year round pet health concern

Mosquitos get a bad rap, and perhaps rightly so. In addition to being annoying, their bites can be uncomfortable and even dangerous to humans. But did you know that mosquitoes can also transmit a deadly disease to your pet?

Heartworm disease is a severe and potentially fatal condition that affects a pet’s heart and lungs. The prevalence of mosquitoes means that heartworm can be found in all 50 states and Canada, and it can affect dogs, cats, and wildlife. At Bayshore Animal Hospital and Avian Practice, we want to take a moment to answer some common questions about heartworm disease and its prevention.

How is Heartworm Transmitted?

The spread of heartworm involves two host animals and a mosquito, making it a long and complex process. In summary:

  • A mosquito bites and takes a blood meal from an infected animal (wild or domesticated).
  • Heartworm larvae (microfilariae) develop in the mosquito’s body for 10-30 days.
  • The mosquito bites a different animal, depositing the microfilariae onto a new host. From there, they enter the bloodstream where they circulate and develop further for several weeks.
  • Eventually, they make their way to the heart and lungs where they mature into foot-long, adult heartworms capable of reproduction.
  • The adult heartworms release new microfilariae into the animal’s bloodstream. There, they can be picked up by another mosquito and transmitted to other potential hosts.

Adult heartworms generally live 5-7 years in dogs and 2-3 years in cats, and they can infect any breed, age, or size of pet.

Signs of Heartworm Disease in Pets

Signs of heartworm disease may be subtle and look like symptoms of other diseases. In the early stages, dogs and cats may not have any symptoms at all, which is why early detection and yearly heartworm testing is vital. As the infection progresses, signs may include:

  • Exercise intolerance
  • Coughing
  • Lethargy
  • Inappetance
  • Difficulty breathing
  • Weight loss
  • Abnormal respiratory sounds
  • Collapse
  • Sudden death


Diagnosing heartworm disease depends on having a complete and accurate medical history, physical exam, and certain diagnostic tests, including:

  • Blood antigen test
  • Blood antibody test
  • Chest radiographs
  • Cardiac ultrasound or echocardiogram


For dogs, treatment involves injections that kill the adult heartworms. Because dead and dying heartworms can cause blockages in your pet’s pulmonary arteries, there’s always a serious risk to treatment. Dogs are typically hospitalized during treatment for close observation. Exercise is restricted (often for several weeks), so as not to exacerbate complications.

Unfortunately, there is no approved drug treatment for cats. Usually, symptoms are treated with the hope that a cat will outlive the worms, but a respiratory emergency and sudden death are very real possibilities.

(Heartworm) Prevention is the Best Medicine

The good news about heartworm disease is that it’s entirely preventable with year-round protection.

Monthly topical or chewable preventives are safe, easy, and effective. Because the life cycle of a heartworm takes about 51 days to complete, it’s important to interrupt this each and every month by administering heartworm prevention medication on a strict schedule.
Please give us a call if you have specific questions or concerns about heartworm disease. Our team is always here to help!